The present invention relates to a method for determining exposure amount in an image copying apparatus, and more particularly to a method for determining exposure amount in an automatic photographic printing apparatus (automatic printer) for printing an image on a color print paper from a photographic color film or the like. Description of the Related Art:
A color negative film as a whole allows three colors of light, blue (B), green (G), and red (R), to be transmitted therethrough, and it is empirically known that the ratios of transmittance of the three color components are, in general, substantially equal or at a fixed rate. For this reason, in an automatic printer an amount of light for printing (i.e., exposure amount) is determined on the basis of the following formula: EQU logFj=Kj+Dj . . . . . . . . . . . . . . (1)
where logF is a logarithm of an amount of light for printing, K is a constant, D is a large area transmittance density (LATD) of the negative measured by a photometric system; and j is the light of any one of the colors B, G and R.
However, if the quantity of light for printing is controlled in an automatic printer on the basis of the aforementioned Formula (1), the overall density of a print from an underexposed negative becomes high in comparison with a print from an adequately exposed negative, while the density of a print from an overexposed tricolor normalized data becomes low. For this reason, exposure amount is determined by providing a slope control circuit so as to correct Dj in Formula (1). Meanwhile, in an automatic printer provided with the slope control circuit, as described above, a faulty print in which the color balance is inappropriate is liable to occur in the case of negatives which have undergone a substantial change over time, negatives photographed with a light source (fluorescent lamp, tungsten lamp, or the like) substantially different from daylight (negatives using a different type of light source), negatives in which color failures have occurred, and other similar negatives. In addition, with a type of film whose manufacturer or sensitivity differs (film of a different type), the sensitivity and density of the three photosensitive layers differ, and favorable prints cannot be made under the same printing conditions. For this reason, Dj in Formula (1) is corrected (color corrected), and in the case of films of a different type, the value of the slope control circuit is altered so as to determine exposure amount. At this time, with respect to a normal correction, an overcorrection is referred to as a high correction, and an undercorrection is referred to as a lowered correction. In the case of the high correction, a color failure occurs, and in the case of the lowered correction, the accuracy of R, G, and B deteriorates.
In recent years, however, high-sensitivity films, films of different usages, novel films with various improvements made have been put on the market every year by various manufacturers, so that the number of film types has increased remarkably and presently several dozens in number. However, since the conditions of print exposure of the various types of film are not necessarily the same, it is necessary to determine the conditions of print exposure for each film type. The operation of determining the conditions of print exposure is generally carried out on a trial-and-error basis and requires trained skill and much time. Therefore, the following techniques have been proposed for automatically determining appropriate conditions of print exposure for each film type on the basis of one set of reference conditions of print exposure.
Japanese Patent Publication No. 15492/1981 discloses a technique in which by making a comparison between predetermined fixed values and color density ratios, B/G, G/R, and R/B, of photometric values at respective points of an image, an examination is made as to whether or not a photometric value of one of the three primary colors is greater than those of the others, and the larger photometric values are not used in determining exposure amount. In addition, Japanese Patent Laid-Open No. 94927/1976 discloses a technique in which the exposure amount is determined on the basis of a photometric value excluding a photometric value which is offset by a predetermined amount from a reference value inherent in a standard image of each film type. These techniques have a drawback in that since it is necessary to provide comparative values or reference values peculiar to the types of film, it is necessary to input data indicating the film type and prepare and store comparative values or reference values for each film type.
To overcome this drawback, Japanese Patent Laid-Open No. 93448/1990 discloses a technique in which a multiplicity of image densities are stored in advance for the respective types of film in correspondence with codes each indicating the film type recorded on the film, and a reference value is determined in advance for each film type on the basis of the stored data, a type of film to be printed being determined by reading the code, thereby determining exposure amount for the film to be printed on the basis of a photometric value of the film to be printed and determined by selection with respect to the reference value and on the basis of a reference condition of print exposure. According to this method, although it is possible to automatically determine a reference value, there is a drawback in that the method cannot be applied to those types of film that are not provided with information such as a code indicating a film type (for instance, in the case of 110 film, Brownie film, and disk films).
As a method for determining print exposure without using information on the film type, a method is known (Japanese Patent Laid-Open No. 46741/1980) in which each time an original film is copied, a photometric value is selected by using a curve indicating a color balance characteristic determined on the basis of photometric values, so as to determine an exposure amount. However, since the color balance characteristic curve is determined on the basis of a test exposure portion burned in the film, this method is very difficult to adopt in practical applications.
In the technique disclosed in Japanese Patent Laid-Open No. 110829/1979, exposure amount is determined on the basis of a multiplicity of photometric values of one film image, and it is necessary that the photometry of one film be completed prior to printing. For this reason, in an apparatus in which a photometric portion and a printing portion are separated from each other as in the technique disclosed in Japanese Patent Laid-Open No. 220761/1984, or in an apparatus in which a photometric portion and a printing portion are provided in the same location as in the technique disclosed in Japanese Patent Laid-Open No. 1648/1986, the film which has been conveyed for both photometry and printing needs to be conveyed in a reverse direction, so that a high-speed operation becomes difficult. In addition, there is another drawback in that since the frequency of conveying the film increases, the film is liable to become damaged.
In addition, Japanese Patent Laid-Open No. 220760/1984 discloses the following technique. A point of the lowest density, including a mask density, is first determined in an original picture, or its vicinity, of a film strip. With an increase in the neutral density at a measuring point with respect to the aforementioned point of the lowest density, a threshold value of chromaticity at that measuring point is increased. Then, a comparison is made between the aforementioned threshold value and a value for the lowest density among measured values obtained by scanning the copied original picture with respect to the three primary colors, thereby selecting a photometric spot which does not exceed the aforementioned threshold value. This technique is based on the fact that the lowest density at a measuring point on an original picture or its vicinity (or the film strip to which the original picture belongs) is close to the mask density, and therefore the chromaticity at individual measuring points is not large.
With this method, however, the following drawback is encountered. That is, from the mask density it is impossible to ascertain the film characteristics (tricolor sensitivity balance, tricolor gradation balance, the linearity of the characteristic curve, etc.). For that reason, a method is provided for determining a threshold of a measuring point with respect to the point of the lowest density, but this method is inadequate in coping with the effect accruing from such as a change in the film type or the negative development performance, a difference between photometers, and so on. Therefore, the above-described color balance characteristic curve is determined with respect to a selected value of the photometric spot (photometric value). For that reason, however, the drawback described in connection with Japanese Patent Laid-Open No. 110829/1979 remains unresolved.
Meanwhile, in order to effect printing in such a manner that the quality of color prints is always excellent in an automatic printer, it is necessary to accurately set the conditions of exposure in the automatic printer. Therefore, standard conditions of exposure are set at the time of installation of the automatic printer. However, it is necessary to reset the conditions of exposure by correcting the same in cases such as where a color paper of a different emulsion number is used, a printer lamp is replaced, the developing solution of the developing equipment is replaced, the contents of the photograph have changed from those having colorful hues to those having obscure hues, or vice versa, during a change of season. In correcting the conditions of exposure, by using a condition-setting film, such as a reference negative film in which a portion corresponding to a negative with a yellowish green object photographed thereon is provided around a portion corresponding to a negative with a gray object photographed thereon, or a film with an image of a standard object photographed thereon, a comparison is made between the density of a test print obtained from this condition-setting film on the one hand, and the density of a reference print obtained in advance and serving as a reference on the other.
Since exposure control is effected on the basis of high correction in the method (photometric point selecting system) for determining exposure amount by selecting photometric points as described above, and on the basis of lowered correction in the case of manual printing, in cases where automatic printing and manual printing are carried out in mixed form with an automatic printer of the photometric point selecting system, it is necessary to set two exposure conditions, one for automatic printing and another for manual printing.
With the above-described photometric point selecting system, however, there is a problem in that unless film characteristics (sensitivity of three colors, gradation, and mask density) are stored accurately in memory, exposure conditions are set with part of the photometric values of a condition setting film discarded, making it impossible to set the exposure conditions properly and undermining reproducibility. This problem is particularly liable to occur in over-exposed and under-exposed negatives. Furthermore, even in the case of a film with a standard object photographed thereon, the image is composed of a multiplicity of colors, the reproducibility of photometric values is poor, and there are cases where it is impossible to set the exposure conditions properly.
In addition, with the method (photometric point selecting system) for determining exposure amount by selecting photometric points, a condition for selecting photometric points is set on the basis of photometric data. However, a problem exists in that it is impossible to obtain a condition for selecting photometric points with good accuracy since the condition for selecting photometric points is set by including photometric data on a special object (e.g., an object in which color failures are liable to occur, an object photographed with a different type of light source, etc.) and also including photometric data on an object with a biased color balance which is peculiar to a local scene (e.g., a seashore, a snowy mountain, tinted autumnal leaves, a forest, etc.).